Journal of Superconductivity and Novel Magnetism最新文献

A theory for cuprate superconductivity predicts the existence of nano-sized loop currents called “spin-vortex-induced loop currents (SVILCs).” In this work, we first calculate magnetic fields produced by them in a single bilayer Bi(_2)Sr(_2)CaCu(_2)O(_{8+delta }) (Bi-2212) thin film for the purpose of detecting the SVILCs. The estimated magnitude of the magnetic field at the point 10a (a is the lattice constant of the CuO(_2) plane) above the surface could be in the order of 100 mT; thus, they may be detectable by currently available detection methods. Next, we investigate the use of them as qubits (the “SVILC qubits”) in an architecture composed of three nano-islands of the thin film and consider the use of the detection of the magnetic field generated by the SVILCs as the qubit readout. We show there are a number of energy levels suitable for qubit states that can be manipulated by external current feeding, and the magnetic field generated by the SVILCs is large enough to be used for the readout.

Besides noticeable challenges in implementing low-error single- and two-qubit quantum gates in superconducting quantum processors, the readout technique and analysis are a key factor in determining the efficiency and performance of quantum processors. Being able to efficiently implement quantum algorithms involving entangling gates and asses their output is mandatory for quantum utility. In a transmon-based 5-qubit superconducting quantum processor, we compared the performance of quantum circuits involving an increasing level of complexity, from single-qubit circuits to maximally entangled Bell circuits. This comparison highlighted the importance of the readout analysis and helped us optimize the protocol for more advanced quantum algorithms. Here, we report the results obtained from the analysis of the outputs of quantum circuits using two readout paradigms, referred to as “multiplied readout probabilities” and “conditional readout probabilities.” The first method is suitable for single-qubit circuits, while the second is essential for accurately interpreting the outputs of circuits involving two-qubit gates.

Structural, electrical, magnetic, and ⁵⁷Fe Mössbauer studies on lanthanum (La)-doped DyFeO₃ (Dy_1-xLa_xFeO₃) are reported in this paper. X-ray diffraction measurements confirm the lattice expansion with La doping. Raman spectroscopic studies give insights into the doping of La into Dy in DyFeO₃. The temperature-dependent magnetization studies of samples show that there is a shift in the spin-reorientation transition temperature (T_SR) towards the lower temperatures with the increase of La-doping concentration for pure DyFeO₃ (DFO), Dy_0.8La_0.2FeO₃ (La2), and Dy_0.6La_0.4FeO₃ (La4) samples which could be due to the weakening of Fe³⁺-Dy³⁺ exchange interaction. Isothermal magnetization data and magnetically split sextet ⁵⁷Fe Mossbauer spectra of all the samples confirm the presence of antiferromagnetic ordering at room temperature. In addition, the observed magnetization data of LaFeO₃ (x = 1.0) sample indicates the presence of spin-glasslike behavior. It is also observed that with the increase of La doping, porosity increases resulting in the enhancement of leakage current density. Ohmic and space charge limited conduction (SCLC) mechanisms explain the conduction mechanism present in the samples.

In a recent paper (Boebinger et al. Nat. Rev. Phys. 7, 2 2025; 2024), fifteen prominent leaders in the field of condensed matter physics declare that hydride superconductivity is real, and urge funding agencies to continue to support the field. I question the validity and constructiveness of their argument.

Nanocrystalline Zn_xCo_1-xFe_2-xAl_xO₄ with particle sizes between 6 and 13 nm were synthesized by glycol-thermal reaction under a low reaction temperature of 200 °C. XRD analysis confirmed the cubic spinel phase with no impurity phases of the as prepared compounds. Raman active photon modes observed also confirmed ferrite crystal lattice. Direct TEM measurements of particle sizes relate well with XRD data and reveal nearly spherical-shaped particle images. Electron spin resonance analysis shows the novel low-field microwave absorptions (LFMA) for the as-prepared (6 ≤ D ≤ 13 nm) compounds recorded at about zero fields. Similar signals have been observed for similar compounds produced by standard ceramic process, confirming reproducibility. The area of the LFMA signals increases with increasing Zn²⁺ and Al³⁺ concentrations and their orientations change with particle size. The presence of LFMA signals makes compounds investigated suitable for applications in low magnetic field sensors, magnetic field-controlled absorbers, spin valves, etc.

This manuscript investigates the magnetocaloric effect and magnetic properties of the Gd(_3)In compound as functions of magnetic field and temperature using a mean-field approximation. We first introduce the model and methodology, followed by the determination of the transition temperature through the analysis of magnetization, susceptibility, and magnetic entropy change ((-Delta S_m)). Our temperature-dependent magnetization analysis reveals a second-order phase transition from the ferromagnetic (FM) to the paramagnetic (PM) phase at 208 K, consistent with previous theoretical and experimental findings. The maximum magnetic entropy change ((-Delta S_m^{text {max}})) is 6.46 J/kg.K at 208 K under a 5 T magnetic field, with a corresponding relative cooling power (RCP) of 680.11 J/kg. Additionally, hysteresis behavior is observed at various temperatures. These findings suggest that Gd(_3)In is a promising candidate for magnetic refrigeration applications.

This paper introduces an ab initio theoretical investigation employing the Full-Potential Linear Augmented Plane Wave (FP-LAPW) method grounded in Density Functional Theory (DFT). The aim is to ascertain the structural and electronic characteristics of the perovskite compounds MgSnO₃ and CaSnO₃. The calculation of structural and electronic properties involved employing the Generalized Gradient Approximation (GGA) for exchange–correlation energy. Through the minimization of energy with respect to volume using the Murnaghan equation of state, the study derived the equilibrium lattice parameter and cohesive properties of the compound. The analysis of the electronic structure was centered on examining the electronic density of states (DOS). Density Functional Theory (DFT) was employed to calculate the pressure and temperature-dependent variations in specific heat, entropy, and Debye temperature. The equation of state, implemented through the GIBBS program based on the quasi-harmonic Debye model, facilitated these computations. Notably, a specific heat behavior of Cv≈Cp was identified at temperatures below T = 300 K, surpassing Dulong-Petit limit values reported for simple perovskites. Furthermore, thermoelectric properties were assessed using the Boltzmann transport theory in the BoltzTraP code.

The resistive transition, under an external magnetic field, was measured for two SmFe_1-xCo_xAsO superconducting films with different quality of intergranular coupling. It is observed that the sample with a low density of intergranular coupling has a semiconducting character and the transition to the long-range superconducting state is controlled by the thermal activated phase slip of the order parameter, described by the Ambegaokar-Halperin model. While in the sample with an intergranular coupling characterized by metallic connectivity, it is the freezing of the vortex lines into a vortex glass phase that controls the transition to the long-range superconducting state. A true superconducting state is observed only in the sample that shows a vortex glass phase. In contrast, in the sample in which the resistivity in the normal state indicates a semiconducting granular coupling, a broad transition that does not reach the zero-resistance state occurs. In fact, in this last sample at high applied fields, the long-range superconducting state is not reached because the intergranular coupling is broken, and the resistive signal associated with the thermal activated flux creep of the bulk vortices becomes dominant.

The structural, mechanical, optoelectronic, magnetic, and thermodynamic properties of the intermetallic compounds GdM₂ (M = Fe, Co, Ni) have been investigated using the full-potential linear muffin-tin orbital (FP-LMTO) method within the local spin density approximation (LSDA) and LSDA + U approaches. In the ferromagnetic phase, both functionals were employed to account for the Coulomb repulsion among electrons of the same atom through the Hubbard U term. These methods were specifically applied to describe the Gd–4f electrons in the electronic and magnetic calculations of ferromagnetic Laves-phase GdM₂ (M = Fe, Co, Ni). Our findings reveal that the LSDA + U approach provides the most stable phase for all the studied compounds. The elastic constant C44 C_{44}C44 indicates that resistance to unidirectional compression is greater than resistance to shear deformation. While LSDA accurately reproduces experimental lattice constants, LSDA + U slightly overestimates them. However, LSDA + U delivers a more precise description of the band structure, density of states, and magnetic moments compared to LSDA. Additionally, a stronger hybridization interaction is observed between Gd-d and Ni-d electrons compared to Gd-d and Co-d, with the weakest interaction occurring between Gd-d and Fe-d electrons. The calculated lattice parameters for GdFe₂, GdCo₂, and GdNi₂ deviate from experimental values by only 0.3%, 0.4%, and 0.2%, respectively, demonstrating a high degree of accuracy. A critical pressure of 10 GPa was found for GdNi₂, indicating a relatively low pressure is needed to transition from the ferromagnetic phase to a non-magnetic state. The calculated total magnetic moments range from approximately 6.5 μB to 7.2 μB per formula unit, with the LSDA + U method providing a more accurate description of the magnetic ordering.